Concrete is often the preferred material for roadway slabs because it tends to be relatively strong, durable and cost-effective over the life of a roadway or highway. Moreover, a well-designed and well-constructed concrete roadway may be less susceptible to potholes and the need for resurfacing than a comparable asphalt roadway. As a result, major highway systems and other major roadways are constructed of concrete.
A typical method of constructing roadways and highways involves preparing a base that includes a course of crushed rock or other material. A network of reinforcing bar is placed over the crushed rock. The continuous slab of concrete is poured over the reinforcing bar over the base of crushed rock. The continuous slab may be sprayed with a substance that slows the loss of moisture from the concrete. After the continuous slab of concrete is allowed to cure for a selected amount of time, the continuous slab is sawed into individual concrete slabs at a selected distance interval. Concrete cures to about 90% of its strength in about 28 days. Generally, the joints are sawed well before the concrete reaches 90% of its strength while the concrete is “green.” The expansion joints are formed between the individual slabs. Expansion joints usually include gaps between adjacent concrete slabs filled with resilient materials, such as an elastomeric caulk. The caulk expands and compresses in response to the thermal loads on the slabs.
The expansion joints allow the individual concrete slabs to contract in cold conditions and expand in hot conditions with less cracking or buckling in the individual concrete slab formed. In other words, separating the continuous concrete slab into individual concrete slabs reduces the number of cracks in the concrete resulting from thermal cycling of the concrete between cold conditions and hot conditions. Annual temperature variations in many areas have a range exceeding 95 degrees Fahrenheit (60 degrees Celsius).
The smaller individual concrete slabs can shift relative to one another over time. Dowels are used to join the individual slabs and prevent the shifting of slabs with respect to one another. Dowels also aid in transferring the load from one individual concrete slab onto the next individual concrete slab on a roadway. For example, as the load from a truck or car crosses a joint between two individual slabs, a set of dowels embedded into the roadway between the two slabs transfers the load from the first slab to the second slab. The dowels also prevent shifting between the slabs. The dowels reduce the effect where a car or truck feels a rhythmic bouncing or thumping at each joint as it travels down the highway.
Currently, the dowels are formed of steel. Even though the dowels are embedded in the concrete between slabs, moisture from rain or other sources reaches the dowels and the dowels corrode. Eventually, as a result of the corrosion, the dowels fail. In colder climates, salt is spread on the roadway to lessen the amount of ice on the roadway. Salt lowers the melting point of water so that ice, if formed, must be at a much lower temperature. The salt used on the roadways speeds the corrosion of the dowels, and shortens the life of the dowels. Once the dowels fail, the concrete roadway is much more prone to misalignment between individual slabs. In addition, the individual slabs may also crack and fail in other ways after a dowel or set of dowels fail.